The venous vasculature is made from thin walled vessels which can hold a variable amount of blood. In the physiologic setting, venous pressure is low, but usually positive. Hence, the veins are distended up to some degree and the blood can flow back to the heart almost without resistance.
In open heart surgery the situation is different for a number of reasons. First, the entire systemic blood flow which is usually brought to the heart by several veins (inferior vena cava, superior vena cava, sinus venosis, thebesian veins, etc.) has to be drained towards the pump oxygenator through one single venous line and one or two venous cannulas. Moreover, for remote venous cannulation, the access vessel is relatively small, as compared to the central portion of the inferior vena cava, and therefore, unphysiological negative pressure has to be applied in order to suck the blood through a relatively narrow venous cannula. Even with central cannulation of the right atrium, only relatively short cannulas are used which drain the heart at the level of the right atrium and a part the inferior vena cava, typically at the level of the liver. The remainder of the venous system remains unsupported and collapses in regular fashion during the extracorporeal circulation. This phenomenon is well known and described by the term “atrial” chatter.
With bicaval central cannulation, the situation is most often worse, because the caval veins are supported only for a few centimeters and the remainder collapses as a function of the negative pressure applied. Major volume loss at the time of passing from partial cardio-pulmonary bypass (unsnared venae cavae) to total cardio-pulmonary bypass (snared venae cavae) is a well known problem and sometimes difficult to solve. Often, venous return must be augmented for open heart surgery with cannulation. (Jeger et al. European Journal of Cardio-thoracic Surgery 16:312-316 (1999), incorporated herein, in its entirety.)
Accordingly, inadequate venous drainage during cardio-pulmonary bypass has many drawbacks (Eur. J. Cardiothorac. Surg., June 2007; 31: 1044-1051). As a matter of fact, the amount of venous blood drained from the patient not only determines the pump flow that can be achieved during cardiopulmonary bypass (CPB) and is crucial for adequate end organ perfusion, but also defines the amount of blood that stays in the patients cardio-vascular system during the procedure. Hence, in addition to superior perfusion, improved venous drainage has also the potential to simplify the surgical procedure (Eur. J. Cardiothorac. Surg., March 2008; 33: 418-423). Considering the on-going trend towards minimal access procedures, the latter aspect is of prime interest (Ann Thorac Surg 2001; 72: 1772-1773).
There are numerous factors that can influence the quality of venous drainage during CPB including venous cannula design, venous cannula positioning, pump set-up etc. (Cardiothorac. Surg., June 2007; 31: 1044-1051). For remote venous cannulation (i.e. trans-femoral or trans-jugular) long thin walled, rectilinear venous cannulas are traditionally used in conjunction with a centrifugal pump or vacuum for augmentation of flow (Ann Thorac Surg 2001; 72: 1772-1773; ASAIO J 2001; 47: 651-654). In this setting the multi-orifice cannula tip is usually positioned in the right atrium and the entire blood flow has to travel through the long and relatively narrow cannula lumen, which is essentially a function of the access vessel diameter. Unfortunately, only about 90% of the theoretical target pump-flow can be achieved with this technique (J Extra-Corpor Technol 2003; 35: 207; Ann Thorac Surg 68: 672-677).
Throughout this description, including the foregoing description of related art, any and all publicly available documents described herein, including any and all U.S. patents, are specifically incorporated by reference herein in their entirety. The foregoing description of related art is not intended in any way as an admission that any of the documents described therein, including pending United States patent applications, are prior art to embodiments of the present disclosure. Moreover, the description herein of any disadvantages associated with the described products, methods, and/or apparatus, is not intended to limit the disclosed embodiments. Indeed, embodiments of the present disclosure may include certain features of the described products, methods, and/or apparatus without suffering from their described disadvantages.